Welcome!

I also am a "plain-clothes commuter". In the winter, unless it's extremely cold, I'll wear my work slacks and shirt (business casual), and over 4 years I've pretty much worked out the right layering, so I don't sweat much either, therefore I don't have to worry about changing! In the summer, I just wear shorts and a jersey (or just a T-shirt) and keep some clothes at work. I think it's a nice perk of a short commute (mine is just over 5 miles) that you don't have to worry so much about cycling-specific clothing. I haven't even gone beyond platform pedals yet, which allows me to wear boots in the winter for warmth.

My white-collar office environment does not seem to be a good one for converting people, for the most part. Many of them live over 20 miles away! I'm the only year-round full-time bike commuter in my building of maybe 150 people, but there is one other who rides in nice weather, and I like to think I've encouraged him a bit. Sometimes I wonder if my continuing to ride through the winter becomes counter-productive, because then they all just think I'm crazy. But maybe at least that'll make the idea of riding in nice weather seem less radical.

I also think I'm the reason the current building has a bike rack, since it is a new building that we moved to after I started bike commuting.

My current evangelization is through a Bike Commuting Group on Meetup.com!